Anthropologists have found the oldest skull of one of our earliest human ancestors. The 3.8 million-year-old fossil changes our understanding of human history.

A facial reconstruction of the 3.8 million-year-old Australopithecus anamensis specimen found in Ethiopia in 2016.Matt Crow, courtesy of the Cleveland Museum of Natural History. Facial reconstruction by John Gurche.

Anthropologists have found very few fossils of the
Australopithecus anamensis species - a hominin ancestor that
lived in Africa between 4 million and 2 million years ago.

Now researchers have discovered that an Australopithecus
anamensis skull found in 2016 is 3.8 million years old, making it
the oldest Australopithecus skull ever found.

The skull, named "MRD," was discovered in the Afar region of
Ethiopia.

Its age indicates that Australopithecus anamensis coexisted
with Australopithecus afarensis, a species that anthropologists
thought lived later on.

Everything we know about the group of human ancestors called
australopiths comes from just a few dozen fossils.

But a skull discovered in Ethiopia is now changing
anthropologists' understanding of the group.

The skull, nicknamed "MRD," was unearthed in 2016 in the Afar
region in Ethiopia. By dating minerals
in the rocks near where MRD was found, scientists determined
the fossil to be roughly 3.8 million years old. That makes it the
oldest Australopithecus skull ever found, edging out the previous
record holder by about 200,000 years.

The scientists' findings about the MRD, published today in the
journal Nature, also show that it belonged to a member of the
oldest species of australopith, called Australopithecus
anamensis.

That means MRD (the nickname comes from its collection number,
MRD-VP-1/1) coexisted with another species of human ancestor,
Australopithecus afarensis, for at least 100,000 years. The
nearly complete skeleton "Lucy" was a member of that latter
group, which roamed Africa between 3.9 million and 3 million
years ago.

The overlapping timelines of these two species alters scientists'
timeline of human evolution, since they previously thought the
species burst onto the evolutionary scene one after the other.

A face for Australopithecus anamensis

A side view of the Australopithecus anamensis skull known as "MRD," which was discovered in Ethiopia in 2016.Dale Omori, Courtesy of the Cleveland Natural History Museum

The term hominin refers to any ancestor in the human lineage
(including modern-day Homo sapiens) who are more closely related
to each other than they are to chimpanzees. That includes
everything from the stone-tool-wielding Homo erectus to our
Neanderthal cousins.

Australopiths, which were bipedally adept and occasionally
climbed trees, were precursors to human ancestors like
Neanderthals. They form an evolutionary link between the last
common ancestor of humans and chimpanzees and the ancestors of
modern humans.

Scientists previously thought Australopithecus anamensis lived
before other early hominin species. But the 3.8 million-year-old
skull shows that there wasn't a linear transition from one
species to the next, in which MRD-like individuals disappeared
and "Lucy"-like individuals took their place.

"This is a game changer in our understanding of human evolution
during the Pliocene," Yohannes Haile-Selassie, the lead author of
the study, said at a press conference.

An Australopithecus anamensis skull composite, rendered by Jennifer Taylor.Dale Omori and Liz Russell, Courtesy of Cleveland Museum of Natural History

The team's discovery also revealed for the first time what
Australopithecus anamensis' face looked like.

"This is the first specimen to ever give us a glimpse about this
species - previous findings were limited to isolated jaw
fragments, teeth, and one small fragment of an ear bone,"
Haile-Selassie said.

Those previous Australopithecus anamensis specimens, found in
Kenya and Ethiopia, were between 4.2 million and 3.9 million
years old. This new skull is slightly younger, but it's still the
oldest Australopithecus skull ever found -it's almost 200,000
years older than the skull found with the nearly
complete "Little Foot" skeleton, which is 3.67 million years
old.

MRD shows that Australopithecus anamensis had a protruding face
with a prominent forehead and cheek bones, much like other
australopiths in the fossil record.

The Australopithecus anamensis skull.Courtesy of the Cleveland Museum of Natural History

"Australopiths have big, massive faces," Stephanie Melillo, one
of the study's coauthors from the Max Planck Institute for
Evolutionary Anthropology, said at a press conference. Members of
the genus Homo, which includes modern humans, have flatter, more
slender faces by comparison.

The skull also revealed that the species had a small brain, which
aligns with previous assumptions about its placement on the
evolutionary tree between "Lucy"-like australopiths and earlier
hominins that were not bipedal.

MRD lived 3.8 million years ago in Ethiopia

Haile-Selassie knew his team had found something special when a
worker named Ali Bereino stumbled upon a jawbone in the sandstone
near the Woranso-Mille district of Ethiopia on February 10, 2016.

"I couldn't believe my eyes when I spotted the rest of the
cranium. It was a eureka moment and a dream come true,"
Haile-Selassie said in a press release.

They discovered an almost complete skull split into two major
pieces - the upper jawbone was separated from rest of head, he
said. The team then analyzed the fossil specimen for the next few
years, digitally reconstructing the skull's missing pieces and
comparing the renderings with other Australopithecus fossils.
That work led them to determine that MRD belonged to the species
Australopithecus anamensis.

The researchers also concluded that MRD was likely a male and
lived in a dry shrubland habitat.

"This cranium looks set to become another celebrated icon of
human evolution," Fred Spoor, a researcher at London's Natural
History Museum who was not involved in the studies, wrote in an
accompanying
Nature article.

"Its discovery will substantially affect our thinking … on the
evolutionary family tree of early hominins," he added.